#include<iostream>
#include<stdio.h>

using namespace std;


class DYS{
private:
	char *s;
	char c;
public:
	void GetText(int n);
	int CountMistake(int n);
	void PrintText(){
		printf("s = %s",s);
	}

};


int main()
{
	DYS dys;
	int n;

	scanf("%d",&n);
	dys.GetText(n);
	printf("%d",dys.CountMistake(n));

	return 0;
}

void DYS::GetText(int n){
	s = new char[n+1];
	scanf("%s",s);
	getchar();
}

int DYS::CountMistake(int n){
	int count=0;
	for(int i=0;i<n;i++){
		c=getchar();
		if(c!=s[i])
			count++;
	}

	return count;
}